1. Field of Invention
The present invention relates to the field of photography and more specifically to cameras with multiple focal lengths adapted to handle automatically a wide range of exposure conditions, some requiring flash. Still more specifically, the invention addresses difficulties encountered with flash photography at longer focal lengths in cameras that also must perform to users expectations at shorter focal lengths.
2. Description of the Prior Art
It is well known in automatic cameras to vary flash intensity with the distance to a subject. Harvey U.S. Pat. No. 4,470,684, issued on Sep. 11, 1984, for example, discloses a camera having a range finder for determining the subject distance, and a control that limits charging of an electronic flash device according to such distance. The control saves battery power and shortens the wait time between exposures whenever the distance is shorter than the maximum capabilities of the flash. Approaches of this type provide important advantages to photographers, but do not address other problems that result from changes in focal length not necessarily dependent on distance.
Although not common, it is known also to sense focal length, and to warn of conditions that are likely to result in blurred images. Hauser et al U.S. Pat. No. 4,124,857, issued on Nov. 7, 1978, is one example. The Hauser patent discloses a camera that energizes a warning light in the viewfinder when the focal length exceeds a predetermined value likely to result in blurred images. The warning light is deactivated when measures are taken to reduce the risk. The Hauser approach recognizes design difficulties in cameras with multiple focal lengths, but requires operator intervention under those conditions most likely to result in poor photographs.